Currently, a light emitting element using an electroluminescence (EL) of an organic material has attracted attention, as a thin light emitting device.
A so-called organic electroluminescence element (hereinafter, also referred to as an organic EL element) is a thin film type complete solid element in which light can be emitted at a low voltage of approximately several V to several dozen V, has various excellent characteristics such as a high brightness, a high light emitting efficiency, thinness, and lightness. For this reason, recently, the organic electroluminescence element has attracted attention as backlights of various displays, a display plate of a signboard, an emergency light, or the like, a surface light emitting body of an illumination light source or the like.
Such an organic EL element has a configuration in which a light emitting layer formed of an organic material is disposed between two facing electrodes, and emission light generated by the light emitting layer is transmitted through the electrode, and is led out to the outside. For this reason, at least one of two electrodes is configured as a transparent electrode, and the emission light is led out from the transparent electrode side.
On the other hand, a demand for a substantially transparent organic EL element in which two-sided light emission can be performed, increases from the viewpoint of a height of tiling or designability.
In Patent Literature 1, an organic EL element, in which a negative electrode (also referred to as a cathode) is formed of a thin silver film in addition to a transparent positive electrode of the related art (also referred to as an anode) using indium tin oxide (ITO) or the like, and thus, a transparence is improved, and emission light from two sides can be led out, is reported as the organic EL element in which two-sided light emission can be performed. According to such a technology, in a general organic EL element of the related art, it is possible to improve a light transmittance in a visible light range, which is less than 40%, to a light transmittance of greater than or equal to 50%, but a demand for a transparent organic EL element is high.
On the other hand, a demand for tiling a plurality of transparent organic EL elements also increases, but a functional member of a sealing/lead-out electrode or the like is disposed around the light emitting unit, and in general, such a portion has an intrinsic light transmittance, and thus, has transparency which is completely different from that of the transparent organic EL element. For example, in a case of using a metal film such as an MAM electrode (Mo/Al.Nd Alloy/Mo) of the related art, the MAM electrode has low light transmissive properties, and thus, the electrode portion is viewed, and there is uncomfortable feeling in visibility of the entire element. In addition, in a case of using an electrode of a high transparence, such as ITO, as the lead-out electrode, a difference in the transparence with respect to the organic EL element is large, and thus, in reverse, such a portion becomes a direct transmission portion, and according to this, there is also uncomfortable feeling in the visibility, conductivity is low in ITO, and a voltage drop occurs.
In addition, in Patent Literature 2, a technology is disclosed in which an auxiliary electrode using a transparent electrode and a thin metal line is superimposed, and thus, electric resistance decreases, and a moisture penetration inhibitor is used at the time of leading out the auxiliary electrode, but the thin metal line portion has a structure in which the thin metal line portion is drawn out to the outside of a sealing material, and thus, there is a problem in durability, and in the known technology, technological thought of controlling the transparency of the lead-out electrode is not disclosed at all.
Therefore, a demand for a transparent organic EL element including a transparent lead-out electrode, in which durability is excellent, low resistance is obtained, and there is no uncomfortable feeling in visibility of the entire element, is high.